Question

Whats the use of Fourier Transform in Communication and how does it vary with Z-Transform?

Answer 1

The fourier transform converts a time function f(t) into a frequency function\[\phi(j \omega)\]
which is, in effect, its frequency spectrum.
Impedance functions such as filter functions and other network characteristics are frequency functions; so in order to determine the output from such a network for a given input, the spectrum of the input signal must first be found. This frequency function is then multiplied by the network transfer function and the resulting frequency function converted into a time function by the inverse Fourier transform.
You will find a brief outline of the relationship of the Z-transform the the discrete-time Fourier transform here.
http://en.wikipedia.org/wiki/Z-transform

Answer 2

to the discrete*

Answer 3

Thanks @kropot72

Answer 4

You're welcome :)